Plasma supply device

ABSTRACT

A plasma supply device generates an output power greater than 500 W at an essentially constant basic frequency greater than 3 MHz and powers a plasma process to which is supplied the generated output power, and from which reflected power is returned to the plasma supply device. The plasma supply device includes at least one inverter connected to a DC power supply, which inverter has at least one switching element, and an output network. The output network is arranged on a printed circuit board. The output network can therefore be designed low priced and accurately.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119(e) to U.S. PatentNo. 60/951,392, filed on Jul. 23, 2007 and under 35 U.S.C. §119(a) toPCT/DE2007/001775, filed on Oct. 4, 2007. Both of these priorityapplications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a plasma supply device for generating an outputpower greater than about 500 W at an essentially constant basicfrequency greater than about 3 MHz for a plasma process.

BACKGROUND

A plasma supply device is a plasma power supply that supplies plasmaprocesses with power. The plasma supply device operates at a basicfrequency that, when used as a plasma power supply, should only deviateslightly from a theoretical value. Typical basic frequencies are, forexample, 3.39 MHz, 13.56 MHz, 27 MHz, 40 MHz, and 62 MHz. The inverter,which has at least one switching element, generates from the DC signalof a DC power supply an alternating signal that changes its signperiodically at the rate of the basic frequency. For this purpose, aswitching element is switched backwards and forwards between aconducting and a non-conducting state within the cycle of the basicfrequency. An output network generates from the alternating signalgenerated by the inverter a sinusoidal output signal at essentially thepredetermined basic frequency.

A plasma is a special aggregate condition that is produced from a gas.Every gas consists in principle of atoms and/or molecules. In the caseof a plasma, the gas is largely ionized, which means that the atomsand/or molecules are split into positive and negative charge carriers,i.e., into ions and electrons, due to the supply of energy. A plasma issuitable for machining workpieces because the electrically chargedparticles are highly reactive chemically and can also be influenced byelectrical fields. The charged particles can be accelerated by means ofan electrical field on a workpiece, where they can release individualatoms from the workpiece on collision. The released atoms can be removedby gas flow (etching) or coated on other workpieces (production of thinfilms). A plasma can be used to machine extremely thin layers, forexample, in the region of few atom layers. Typical applications forplasma machining are semiconductor technology (coating, etching, etc.),flat screens (similar to semiconductor technology), solar cells (similarto semiconductor technology), architectural glass coating (heatprotection, dazzling protection, etc.), storage media (CD, DVD, harddiscs), decorative coatings (coloured glasses, etc.), and toolhardening. These applications impose high demands in terms of accuracyand process stability.

To generate a plasma from a gas, energy is supplied to the gas. Energycan be generated in different ways, for example, with light, heat, orelectrical energy. If energy is generated using electrical energy, thenthe plasma is ignited with the electrical energy. A plasma for machiningworkpieces is typically ignited in a plasma chamber, for which purposean inert gas, e.g., argon, is generally conducted into the plasmachamber at low pressure. The gas is exposed to an electrical field thatis produced by electrodes and/or antennae.

A plasma is generated or is ignited when several conditions are met. Asmall number of free charge carriers must be present, and in most cases,use is made of the free electrons that are always present to a smallextent. The free charge carriers are accelerated so much by theelectrical field that they release additional electrons when collidingwith atoms or molecules of the inert gas, thus producing positivelycharged ions and even more negatively charged particles (electrons). Theadditional free charge carriers are again accelerated and on collisionproduce additional ions and electrons. An avalanche effect is created.The natural recombination counteracts the constant generation of ionsand electrons, i.e., electrons are attracted by ions and recombine toform electrically neutral atoms and/or molecules. Therefore energy isconstantly supplied to an ignited plasma in order to maintain it.

Plasma power supplies are used for generating or igniting andmaintaining a plasma, but can also be used for exciting gas lasers.Plasma power supplies have the smaller dimensions to ensure that theycan be arranged in the application close to the plasma discharges. Theyshould have the highest possible repeat accuracy and operate precisely,with the smallest possible losses to achieve high efficiency. Furtherrequirements are minimal production costs and high maintenancefriendliness. If possible, plasma power supplies are provided withoutmechanically driven components, and fans can be undesirable because oftheir limited life and the risk of contamination. Furthermore, plasmapower supplies should be as reliable as possible, should not overheat,and should have a long operating time.

Due to the high dynamics and often chaotic conditions in plasmaprocesses, a plasma power supply is subject to much more stringentrequirements than any other power supply. An un-ignited gas, which hasonly a very small number of free charge carriers, has an almostinfinitely high impedance. Because of its large number of free chargecarriers, a plasma has a relatively low impedance. When the plasma isignited, therefore, there is a rapid impedance change. Anothercharacteristic of an ignited plasma is that the impedance can vary veryquickly and often unpredictably, and the impedance is then said to bedynamic. The impedance of the plasma is still non-linear to a greatextent, which means that a variation in the voltage on the plasma doesnot correlate to a similar variation in current. For example, thecurrent can increase much more quickly as the voltage increases due, forexample, to an avalanche effect, or the current can also decrease as thevoltage increases at so-called negative impedance.

If a power supply discharges a power in the load direction, such as aplasma load, which flows at finite speed towards the load, but cannot beabsorbed there because the same current is not set when the voltage ispresent on the load due to the different impedance, only that proportionof the power that is calculated from voltage and current to obtain theload is absorbed, the remaining proportion of the power being reflected.In fact this also takes place in power supplies with low frequencies,and also in direct current, but only in the latter does it take place soquickly that the voltage at the output of the power supply has inpractice not yet changed by the time the reflected energy returns. Tothe observer, therefore, this happens simultaneously. However, in highfrequency technology with frequencies above around 1 MHz, the voltageand current at the output of the power supply have generally alreadychanged by the time the reflected power returns.

The reflected power has a considerable influence on the power suppliesin high frequency technology. Reflected power can destabilize powersupplies and prevent the supply systems from operating according to theregulations. Because of incorrect adaptations, the reflected power onlyhas proportions of the basic frequency at constant impedances. Thereflected power cannot be blocked or absorbed with filters becausefilters cannot distinguish between forward (to the load) running wavesand backwards (from the load) running waves, and would consequently alsoblock or absorb the forward running waves. In order to reduce orminimize the reflected power, so-called impedance adapter elements ornetworks are used. Impedance adapter elements or networks can beproduced using high frequency technology by combinations of inductances,capacitances, and resistances, with resistances not being absolutelynecessary. However, if the load is not a constant impedance, but is adynamic and non-linear impedance, at least two additional problematicphenomena can arise. First, energies can be generated by the non-linear,dynamic impedance at frequencies that differ from the basic frequency,and proportions of these frequencies are conducted in the direction ofthe power supply. These are blocked or absorbed by filters. Second, theimpedance adapter elements cannot follow the fast dynamic impedancevariations sufficiently quickly, thus giving rise increasingly toreflections at the basic frequency, which reflections are conducted bythe dynamic impedance to the power supply.

Unlike in other power supply systems, plasma power supplies need to beable to be loaded with any incorrect termination, from no load throughshort-circuit, from infinitely high capacitive load to infinitely highinductive load. At any point on the Smith graph, a plasma power supplymust be able to supply power for at least a short period of time andmust not suffer permanent damage in doing so. This is linked to the highdynamics and the often chaotic conditions in a plasma process. Inaddition, frequencies within a wide range and differing from the basicfrequency can occur, and these frequencies should be prevented fromcausing permanent damage to the plasma power supply. The detection andrapid disconnection of an incorrect terminal are allowed in this case,but the plasma power supply should not be damaged if at all possible.

SUMMARY

In some general aspects, a plasma supply device generates an outputpower greater than 500 W at an essentially constant basic frequency ofgreater than 3 MHz and powers a plasma process, to which the generatedoutput power is supplied, and from which reflected power is returned tothe plasma supply device. The plasma supply device includes at least oneinverter connected to a DC power supply, where the at least one inverterhas at least one switching element, and at least one output networkelectrically coupled to the at least one inverter. The at least oneoutput network is arranged on a printed circuit board.

Implementations can include one or more of the following features. Forexample, the plasma supply device can include at least one inputconnection arranged on the printed circuit board for connection to theat least one inverter.

The at least one inverter can be arranged on the printed circuit board.

At least one component of the plasma supply device can be designed sothat it at least partially absorbs power reflected from the plasmaprocess at the basic frequency.

The at least one output network can include at least one inductance thathas a planar technology. The at least one output network can include atleast one output transformer having a primary-side winding and asecondary-side winding. The at least one output transformer can beplanar. The printed circuit board can be of multi-layer design. Theprinted circuit board can have four layers, and a turn of the at leastone output transformer can be formed in each of the four layers of theprinted circuit board. The primary-side winding and the secondary-sidewinding of the at least one output transformer can each have two turns.The at least one output network can include at least one set of firstinductances arranged between the input connection and the primary-sidewinding.

The printed circuit board can be produced from glass fiber reinforcedepoxy resin. The printed circuit board can be made of FR4 or FR5material.

The at least one output network can include at least one inductancehaving a value greater than 50 nH and a quality better than 200.

The distance between at least two layers of the printed circuit boardcan be greater than a distance required for the electric strength of theat least two layers.

The plasma supply device can include capacitances formed between turnsof the secondary-side winding of the at least one output transformer,and an LC filter can be formed from the capacitances between the turnsof the secondary-side winding of the at least one output transformer andfrom the inductance of the secondary-side winding of the at least oneoutput transformer. The plasma supply device can include anothercapacitance formed between the primary-side winding and thesecondary-side winding of the at least one output transformer, where theother capacitance can be a component of the LC filter.

The at least one output network can include at least one impedanceadapter element between the secondary-side winding and at least oneoutput connection for the connection of a load, where the at least oneimpedance adapter element can include one or more of a second inductanceand a capacitor. The capacitor can have a planar technology. Thecapacitor can be a surface mount device.

The plasma supply device can include through contacts formed on theprinted circuit board for connecting conductor paths arranged in thelayers.

The plasma supply device can include at least one magnetic fieldstrengthening element assigned to one or more of the inductances. Theplasma supply device can include at least one magnetic fieldstrengthening element assigned to one or more windings of the at leastone output transformer. The at least one magnetic field strengtheningelement can be a ferrite.

At least one recess can be formed on the printed circuit board forreceiving the at least one magnetic field strengthening element.

The plasma supply device can include a cooling plate connected to theprinted circuit board. The printed circuit board can be separated fromthe cooling plate by, for example, a distance of between about 5 mm toabout 20 mm. The printed circuit board can be separated from the coolingplate by a distance that is in relationship to the thickness of amagnetic field strengthening element enclosing one or more ofinductances and windings of an output transformer. The plasma supplydevice can include one or more heat transmission elements between theprinted circuit board and the cooling plate. The heat transmissionelements can be in the vicinity of the at least one output transformer,and conductor paths of the printed circuit board can be guided throughthe magnetic field strengthening element assigned to the at least oneoutput transformer to the heat transmission elements.

The plasma supply device can include an earth connection on the printedcircuit board. The earth connection can be a bore through the printedcircuit board having an electrical contact.

The plasma supply device can include two output networks, each outputnetwork including at least a set of first inductances, an outputtransformer, and an impedance adapter element, where the output powersof the two output networks are combined to one total power with acoupler.

At least two output networks can be present whose output powers arecombined to one total power. The output networks can be connected inparallel to at least one common inverter. The output networks can beconnected to separate inverters. The combination of the output powerscan be achieved by means of at least one coupler. The at least onecoupler can be on the printed circuit board and can be designed at leastpartially in a planar geometry.

In another general aspect, a plasma supply system generates an outputpower greater than 500 W at an essentially constant basic frequency ofgreater than 3 MHZ for powering a plasma process. The plasma supplysystem includes at least two plasma supply devices, and at least onecoupler that combines output powers of the at least two plasma supplydevices. Each plasma supply device includes at least one inverterconnected to a DC power supply, where the at least one inverter has atleast one switching element, and at least one output networkelectrically coupled to the at least one inverter, where the at leastone output network is arranged on a printed circuit board.

In one general aspect, a plasma supply device includes at least oneoutput network that is arranged on a printed circuit board (PCB). Thismeasure enables the output network to be produced extremely cheaply. Itis also possible to produce the components of the output network withexact inductances and capacitances, i.e., inductance and capacitancevalues that in any case deviate slightly from theoretical values. Thisis possible with high repetition accuracy. Furthermore, at least oneinput connection can be arranged on the printed circuit board (PCB) forconnecting at least one inverter and/or at least one inverter can bearranged on the printed circuit board. The output network has aconsiderable influence on reliability and consequently on the life timeof the entire plasma power supply or plasma supply device. At least onecomponent of the plasma supply device can be designed so that it atleast partially absorbs power reflected by the plasma process at thebasic frequency. Here the reflected power can be converted to heat. Thereflected power can be absorbed at least partially by the inverter, bylossy inductances, transmitters, capacitances, or resistances.

In the case of the plasma supply device, the output network isdimensioned so that the area of the printed circuit board (PCB) can bekept smaller than 150 cm². The thickness of the printed circuit board(PCB) is typically 2 to 5 mm. Glass fiber reinforced epoxy resin, forexample, FR4 or FR5 material, can be used as the printed circuit board(PCB) material. These materials are sufficient for this circuit,although they have a more lossy electric behavior and lower thermalconductivity and heat resistance than comparatively much more expensiveceramics or PTFE materials. Multi-layer circuit boards with flatdesigned inductances and surface mount device (SMD) components are knownfor lower frequency and power ranges. Contrary to the opinion that thematerials used for the printed circuit boards of prior art areunsuitable for high frequency applications with an output power>500 Wand a basic frequency>3 MHz, due to high heat development and bad powerheat discharge, it is proposed to create an output network with planarinductances and capacitances on a printed circuit board (PCB) for theoutput power and high frequency range mentioned. This results inconsiderable savings in terms of space requirement and cost, and inimproved accuracy and reproducibility in the production of the plasmasupply device.

In this description, the terms inductance or capacitance and capacitorrespectively are used for a component arranged on the printed circuitboard (PCB) on the one hand, and for a physical value assigned to thecomponent on the other, the corresponding application being evident fromthe context.

In one design of the plasma supply device, the at least one outputnetwork has at least one output transformer with a primary-side windingand a secondary-side winding. A galvanic separation is made by theoutput transformer between the at least one inverter connected to a DCpower supply and a load, for example, a plasma load, to be connected tothe printed circuit board. In this manner, low frequency signals, inparticular, DC components that can be present at the output of theinverter, are separated. For the galvanic separation, a capacitance canalternatively be used. Due to the formation of adequate safe distances,the primary side of the output transformer can remain galvanicallyconnected to the mains connection (that is, the supply voltageconnection). Because a galvanic separation is correspondingly dispensedwith in the DC power supply, the costs and overall size of the plasmasupply device can be further reduced.

The output transformer can be designed in planar technology. Such anoutput transformer, produced in this manner and arranged on the printedcircuit board, can be manufactured very precisely, and the turns of theprimary- and secondary-side winding can be produced with goodreproducibility. Moreover, this is cheaper than a construction with wirewindings. Furthermore, the output transformer can be constructed with alarge area and hence can be easily cooled.

In a further embodiment, the printed circuit board (PCB) is of amulti-layer design, in particular, with four layers, and one turn of theoutput transformer is formed in each layer of the printed circuit board.This provides the advantage that the capacitive coupling between theturns, which is normally considered to be an undesirable, parasiticcapacitance, can be used for further switching parts, e.g., for animpedance adapter element. In addition, the stray inductances of theoutput transformer can also be used for other switching parts.

In one embodiment, the primary-side winding and the secondary-sidewinding of the output transformer each have two turns. All four layersof the printed circuit board (PCB) can therefore be used. The magneticcoupling and the stray inductance simultaneously generated can form anLC filter, for example.

In one embodiment of the plasma supply device, the output network has atleast one set of first inductances arranged between the input connectionand the primary-side winding. “Set of first inductances” is understoodto mean that each inverter is connected by a first inductance to theoutput transformer assigned to it. The first inductances can be designedas planar conductor paths, each of which has one turn. The firstinductances are suitably coupled magnetically, which means that magneticfield strengthening elements can be dispensed with. However, additionalmagnetic field strengthening elements can increase the inductance evenfurther. Inductances ranging from 50 to 300 nH are obtained. Theinductances can have values higher than 50 nH and qualities (that is,quality factors) better than 200. In one embodiment, conductor paths maybe guided in parallel in several layers, for the first inductances, forexample. The current is distributed to conductor paths and the lossesare smaller. This improves the quality of the inductances to valuesgreater than 200, which was not previously achieved with planarinductances ranging from 50 to 300 nH on only one layer.

The inverter circuit of the plasma supply device can have two halfbridges each of which is connected to the DC power supply. By connectingthe centers of the half bridge circuit by means of the first inductancesto the primary-side winding of the output transformer, a low lossno-volt connection over a wide range of load impedances can be achieved.Advantageous switching conditions can be guaranteed for the inverter bymeans of the plasma supply device. For example, a no-volt connection isadvantageous, particularly at higher frequencies and in the case ofMOSFETs, or a no-current disconnection is advantageous, particularly atlow frequencies and in the case of insulated-gate bipolar transistors(IGBTs) as switches in the inverter. This can be achieved by suitabledimensioning of the output network and the switching parts of the outputnetwork.

The distance between at least two layers of the printed circuit board(PCB) can be considerably greater than the distance required for theelectric strength of the two layers.

In one embodiment of the plasma supply device, the capacitance formed bythe conductor paths between the turns of the secondary-side winding ofthe at least one output transformer, together with the inductance of thesecondary-side winding of the at least one output transformer, forms anLC filter. The capacitance formed by the conductor paths between theprimary-side winding and the secondary-side winding of the at least oneoutput transformer can be another component of the LC filter.

In one design, the output network can have an impedance adapter elementbetween the secondary-side winding and an output connection for theconnection to a load, with one or a plurality of second inductancesand/or one or a plurality of capacitors. A load impedance adapterelement is achieved in this manner from the inverter to the output ofthe output network. The power components reflected and/or generated by aplasma load are filtered by reactive components of the output network,i.e., inductances and capacitances.

Furthermore, the output network can have an LC filter. A signal with arelatively high proportion of harmonics or harmonic frequencies isgenerally transmitted to the output of the inverter, which frequenciesare undesirable at the output of the plasma power supply, i.e., at theoutput connection. The plasma supply device filters these harmonics orharmonic frequencies by means of the LC filter. The stray inductance andthe capacitance between two turns of the output transformer form an LCfilter, thus dispensing with additional components. The LC filter iseither designed as described above and/or is part of the impedanceadapter element. In a further embodiment, the output network has an SMDcapacitor parallel to the secondary-side winding. The capacitancebetween the secondary-side turns can then reinforce the capacitance ofthis capacitor.

Furthermore, the second inductance or inductances can be designed inplanar technology. The capacitor or capacitors can, for example, bedesigned in planar technology and/or as an SMD component. This providesthe advantage of improved accuracy and reproducibility in the productionof the plasma supply device.

The printed circuit boards can have through contacts for connecting theconductor paths arranged in layers. High strength of the printed circuitboard (PCB) and good contacts between the switching parts arranged on itare therefore guaranteed. Both the input connection for connecting theDC power supply or the inverter and the output connection for connectingthe plasma load, to which the sinusoidal output signal generated by theoutput network is transmitted, can be connected to through contacts. Nosuch through contacts could be provided on printed circuit boards fromthe state of the art, which for reasons of thermal conductivity havebeen mounted directly on the cooling plate, because they would havecaused a short-circuit between the cooling plate lying on an earthpotential and the potentials of the through contacts.

In one design of the plasma supply device, at least one magnetic fieldstrengthening element assigned to one or a plurality of inductancesand/or windings of the output transformer, is provided on the printedcircuit board. This enables the number of turns for the individualinductances to be reduced. It is therefore possible to achieve highinductances with short conductor paths. Because of the short conductorpaths, there is the added advantage of low resistances andcorrespondingly lower losses.

A magnetic field B is caused by a magnetic field strength H, which is inturn caused by a current I through a cable that forms an inductance.There is a relation B=μ*H between B and H, where μ is the permeability.The permeability μ is composed of the permeability of the vacuumμ₀=4π*10⁻⁷ Vs/Am and the permeability coefficient μ_(r), which ismaterial-dependent: μ=μ₀*μ_(r). A magnetic field strengthening elementhas a μ_(r) that is far greater than 1. Typically a ferrite is used asthe magnetic field strengthening element at the frequencies mentioned.In the case of inductances the magnetic field strengthening elementincreases the value of the inductance according to the permeabilitycoefficient μ_(r).

In one embodiment, the at least one magnetic field strengthening elementcan be a ferrite, in particular, a perminvar ferrite. Typically themagnetic field strengthening elements or ferrites enclose the conductorpaths of the planar inductances in an annular manner. The ferrites thatenclose the turns of the inductances or windings in an annular or shellmanner suitably consist of two parts that are arranged on the printedcircuit board (PCB) on a counterpart basis.

Furthermore, at least one recess can be formed on the printed circuitboard (PCB) for receiving the at least one magnetic field strengtheningelement. Recesses are typically formed on the printed circuit board(PCB) for receiving the magnetic field strengthening element consistingin two parts of two identical or at least similar parts. The magneticfield strengthening element can in this way be arranged safely on theprinted circuit board (PCB) so that space is saved.

In one embodiment, the plasma supply device has a cooling plateconnected to the printed circuit board. In one design, coolant flowsthrough the cooling plate, thus providing a plasma power supply withoutforced air flow, i.e., without fans. In one design the cooling plate isconnected to an earth potential, which ensures good electrical screeningof the output network.

A distance of 1 μm/V is normally required for sufficient electricstrength as a function of the maximum voltage that can be generatedbetween the conductor paths of two layers of the circuit board. Toprevent excessive heat development when operating the plasma supplydevice, a greater minimum distance between the conductor paths isproposed between two layers, since the electric losses are reduced withthis extended minimum distance. This greater minimum distance istypically 10 μm/V. In one design the printed circuit board (PCB) can bearranged separated from the cooling plate, in particular by a distanceof 5 mm to 20 mm. The inductances can then be provided with a betterquality and low losses.

In one design the output network can be arranged at such a distance fromthe cooling plate, where the distance is related to the thickness of themagnetic field strengthening element enclosing the inductance(s) and/orthe windings of the output transformer. The magnetic field strengtheningelements can enclose the inductances in a rectangular/annular shape andplaced flat on the cooling plate, possibly for mechanical load reliefwith elastic heat transmission elements between the cooling plate andthe magnetic strengthening elements. This ensures good heat discharge ofthe heat developed in the magnetic field strengthening elements. Theconstruction of an output network with the extremely low costmulti-layer FR4 or FR5 material and with through contacts was notpossible until the opinion that the entire printed circuit board (PCB)provided with planar inductances must lie laminar in contact with thecooling plate was departed from.

In one design, one or a plurality of electrically insulating heattransmission elements are arranged between the printed circuit board(PCB) and the cooling plate. The heat is discharged from the printed(PCB) to the cooling plate by means of the heat transmission elements,which are also suitably of an elastic design. The heat is dischargedfrom the points on the printed circuit board (PCB) at which a strongheat development takes place, for example, in the region of the outputtransformer, by means of flat copper conductor paths, to points wherethere is less heat development. The heat transmission elements can bearranged in the vicinity of the output transformer, and conductor pathscan be guided through the magnetic field strengthening element assignedto the output transformer to the heat transmission elements.Electrically insulating heat transmission elements of a flat design canbe arranged in the region of an enclosing magnetic field strengtheningelement, such as a ferrite, i.e., in the region of high currents. Thewarmth or heat is expelled as far as possible from the region of themagnetic field strengthening element by means of the copper conductorpaths, and is discharged further from there to the cooling plate.

An earth connection can be provided on the circuit board. The earthconnection can be designed as a contacted bore. Spacer bolts can beprovided between the printed circuit board (PCB) and the cooling plate,to which bolts an earth connection can be made.

The upper power limit of the plasma supply device is determined, amongother things, by the dissipation to be discharged. The upper power limitcan be increased if the plasma supply device has at least two outputnetworks on a printed circuit board (PCB), and the two output networkstogether can be fed by at least one inverter connected to the DC powersupply or can be individually fed by at least one inverter connected tothe DC power supply, and if their output powers can be combined by atleast one coupler to generate one total power. A coupler is anelectronic component that is designed to combine or split electricalpowers. The coupler can also have components that at least partiallyabsorb the reflected power.

The upper power limit can be further increased if at least one outputnetwork of the plasma supply device has at least two sets of firstinductances and/or at least two output transformers and/or at least twoimpedance adapter elements whose input and output powers are each splitby at least one coupler or combined to form one total power.

The at least one coupler required in these cases can be arranged on aprinted circuit board (PCB) and can preferably be designed at leastpartially in planar technology.

In a plasma supply arrangement the output powers are combined by atleast two plasma supply devices by at least one coupler.

Further features and advantages of the invention are evident from thefollowing description of exemplary embodiments of the invention, withreference to the figures in the drawing, which show the detailsaccording to the invention, and from the claims. The individual featuresmay be implemented individually or several features may be combined in avariant of the invention.

Preferred exemplary embodiments of the invention are representeddiagrammatically in the drawing and are explained in greater detail inthe following with reference to the figures in the drawing.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified circuit diagram of a plasma supply deviceincluding an output network;

FIG. 2 shows a section through a printed circuit board (PCB) with anoutput network arranged on it and through a cooling plate connected tothe printed circuit board;

FIG. 3 a to 3 d each show one layer of the printed circuit board (PCB)of FIG. 2;

FIG. 4 shows a simplified circuit diagram of another plasma supplydevice; and

FIGS. 5 a and 5 b each show a simplified circuit diagram of an exemplaryplasma supply device having two output networks.

DETAILED DESCRIPTION

FIG. 1 shows a plasma supply device 10 having a first inverter 11 and asecond inverter 12. The inverters 11, 12 are designed as half bridges,each with two series-connected switching elements 11.1, 11.2, 12.1,12.2. Both inverters 11, 12 are connected to a positive supply voltageconnection 13 and a negative supply voltage connection 14 of a DC powersupply (not shown). Plasma supply device 10 also has an output network15 to which inverters 11, 12 on one side, and a load 16, for example, aplasma load, on the other side, are connected. Acting as a key part ofthe plasma supply device 10, the output network 15 includes an outputtransformer 17 with a primary-side winding 18 and a secondary-sidewinding 19.

The output network 15 includes first inductances 21 a, 21 b arrangedbetween input connections 20 a, 20 b from respective inverters 12, 11and the primary-side winding 18 of the output transformer 17. The firstinductances 21 a, 21 b are coupled together magnetically (as denoted bydotted line 22) because of their mutual spatial arrangement on a printedcircuit board (PCB) (not shown in FIG. 1). A higher output power can beachieved by means of the plasma supply device 10 by connecting togetheroutputs of the two inverters 11, 12 that are fed respectively throughthe input connections 20 a, 20 b with the primary-side winding 18. Acentral tapping 24 is provided on the primary-side winding 18 by meansof a further connecting cable 23, another inductance 25 being providedin further connecting cable 23, which inductance is connected to aninput connection 20 c, which is connected to the connection point ofinverters 11, 12. The primary-side winding 18 has two primary-side turns26 a, 26 b, which are arranged on both sides of central tapping 24.

An impedance adapter element 28 is arranged between the secondary-sidewinding 19 and an output connection 27 for the load 16. Impedanceadapter element 28 includes a second inductance 29 and two capacitors 30a, 30 b. The impedance adapter element 28 can have a plurality of secondinductances 29 in series with the load 16 and capacitors 30 a, 30 b inparallel with the load 16. The secondary-side winding 19 also has twosecondary-side turns 31 a, 31 b. An alternating current signaltransmitted to input connections 20 a, 20 b is generated in the form ofa sinusoidal output signal transmitted to the output connection 27 bymeans of the output network 15. Furthermore, harmonic frequencies arefiltered and DC proportions separated.

The output transformer 17 is designed with a planar technology in thatprimary- and secondary-side turns 26 a, 26 b, 31 a, 31 b lie flat oneabove the other. Planar technology means that inductances are liketracks on the PCB or several layers of the PCB and they may be curled orhelical to enhance the inductivity. There are capacitances in the formof capacitors 32 a, 32 b, 32 c between the turns 26 a, 26 b, 31 a, 31 bof the output transformer 17. The capacitors 32 a, 32 b, 32 c and theturns 31 a, 31 b of the secondary-side winding 19 are components of anLC filter 33. Furthermore, an earth connection 34 connected to thesecondary-side winding 19 is provided. The other inductance 25 and thesecond inductance 29 each have a magnetic field strengthening element inthe form of a perminvar ferrite. The output network 15 is designedprimarily with a planar technology and is arranged on a multi-layercircuit board, including the input connections 20 a, 20 b, 20 c, theearth connection 34, and the output connection 27.

FIG. 2 shows a vertical section through a horizontally arrangedmulti-layer printed circuit board (PCB) 38. The printed circuit board(PCB) 38 is constructed as a so-called multi-layer printed circuitboard. The printed circuit board (PCB) 38 is separated from andconnected to a cooling plate 40 by means of spacer bolts 39 a, 39 b, 39c. The output network 15 including the input connections 20 a, 20 b andthe output connection 27 are arranged on or in the printed circuit board(PCB) 38, where the input connections 20 a, 20 b connect to theinverters 11, 12 and the output connection 27 connects to the load 16. Afirst magnetic field strengthening element 41 is arranged in the regionof the first inductances 21 a, 21 b, and a second magnetic fieldstrengthening element 42 is arranged in the region of the outputtransformer 17, where the magnetic field strengthening elements 41, 42are each composed of two parts arranged on both sides of the printedcircuit board (PCB) 38. The capacitors 30 a, 30 b of the impedanceadapter element 28 are designed as surface mount device (SMD)components.

Elastic, flat designed heat transmission elements 43 a, 43 b, 43 c arearranged between the printed circuit board (PCB) 38 and the coolingplate 40 in the region or vicinity of the inductances 18, 19, 21 a, 21b, 29 of the output network 15. For example, the elements 41, 42surround the inductances 21 a, 21 b and the output transformer 17 andalso touch the heat transmission elements 43 a and 43 b to provide anindirect thermal coupling between the elements 43 a, 43 b and theinductances 21 a, 21 b and the transformer 17. And, another heattransmission element 44 designed as a copper block is provided in theregion of the impedance adapter element 28 to provide an indirectthermal coupling between the inductance 29 and the heat transmissionelement 44. The heat generated during operation of the plasma supplydevice 10 in the region of inductances 18, 19, 21 a, 21 b, 29 isdischarged from the printed circuit board (PCB) 38 to the cooling plate40 by means of the heat transmission elements 43 a, 43 b, 43 c, 44. Forimproved heat discharge, the magnetic field strengthening elements 41,42 can be surrounded, region by region, by a heat conducting compound,for example, a heating conducting foam. The output network 15 isdesigned in planar technology with conductor paths in the multilayerprinted circuit board (PCB) 38. Through contacts 45 and 45′, forexample, are formed in the printed circuit board (PCB) 38 for connectingthe conductor paths of different layers.

FIGS. 3 a to 3 d show the different layers of the printed circuit board(PCB) 38, namely a lower layer 51 (FIG. 3 a), a first inner layer 52(FIG. 3 b), a second inner layer 53 (FIG. 3 c), and an upper layer 54(FIG. 3 d). Magnetic field strengthening elements 41, 41′, and 42 arearranged in the region of the first inductances 21 a, 21 b and in theregion of inductances the 18, 19 of the output transformer 17 with turns26 a, 26 b, 31 a, 31 b. In addition, a third magnetic fieldstrengthening element 55 is provided in the region of impedance adapterelement 28. Adjacent to through contacts 45, 45′, 45″, 45′″, bores 56,56′, 56″ are formed between the layers 51, 52, 53, 54, thus ensuringgood contacts between the conductor paths and a high strength of theprinted circuit board (PCB) 38. Adjacent to the input connections 20 a,20 b and the output connection 27, the earth connection 34 is arrangedon the printed circuit board (PCB) 38. The capacitors 30 a, 30 b of theimpedance adapter element 28, designed as SMD components, are arrangedon the upper layer 54. A possible layer of the heat transmissionelements 43 b, 43 b′ is drawn in FIG. 3 a. In the output transformer 17,a high current flows through all four layers 51, 52, 53, 54 of theprinted circuit board (PCB) 38. The highest heat development thereforetakes place here. This heat cannot be discharged sufficiently to coolingplate 40 inside the magnetic field strengthening element 42 formed asferrite. Therefore the heat is expelled from the region of magneticfield strengthening element 42 through the conductor paths formed incopper, and is discharged through the heat transmission elements 43 b,43 b′ to the cooling plate 40.

FIG. 4 shows the plasma supply device 10 with the inverters 11, 12connected to supply voltage connections 13, 14 of a DC power supply andwith the output network 15. The output network 15 includes the inputconnections 20 a, 20 b for the input signal generated by respectiveinverters 12, 11, the input connection 20 c for the central tapping, andthe output connection 27 for the connection of the load 16. Theinverters 11, 12, just as the output network 15, the input connections20 a, 20 b, 20 c, and the output connection 27, are arranged on theprinted circuit board (PCB) 38.

FIGS. 5 a and 5 b each show a plasma supply device 10′ with the outputnetwork 15 and another output network 15′. Each of the output networks15, 15′ have three input connections 20 a, 20 b, 20 c and 20 a′, 20 b′,20 c′, respectively. In FIG. 5 a, both output networks 15, 15′ areconnected in parallel to inverters 11, 12 and to DC power supply 13, 14.The plasma supply device 10′ shown in FIG. 5 b is different in that theother output network 15′ is connected by additional inverters 11′, 12′to additional supply voltage connections 13′, 14′ of another independentDC power supply. The output signals of both of the output networks 15,15′ are combined by means of a coupler 59 and are transmitted to theload 16. The output networks 15, 15′, including the coupler 59, arearranged on the printed circuit board (PCB) 38. It is also conceivablefor the inverters 11, 12, 11′, 12′ to be arranged on the printed circuitboard (PCB) 38. It is also conceivable for the coupler 59 to be arrangedoutside the printed circuit board, and it is also possible for theoutput networks to be provided on separate printed circuit boards withor without inverters.

Other implementations are within the scope of the following claims.

1. A plasma supply device for generating an output power greater than500 W at an essentially constant basic frequency of greater than 3 MHzand for powering a plasma process, to which the generated output poweris supplied, and from which reflected power is returned to the plasmasupply device the plasma supply device comprising: at least one inverterconnected to a DC power supply, wherein the at least one inverter has atleast one switching element, and at least one output networkelectrically coupled to the at least one inverter, wherein the at leastone output network is arranged on a printed circuit board.
 2. The plasmasupply device of claim 1, further comprising at least one inputconnection arranged on the printed circuit board for connection to theat least one inverter.
 3. The plasma supply device of claim 1, whereinthe at least one inverter is arranged on the printed circuit board. 4.The plasma supply device of claim 1, wherein at least one component ofthe plasma supply device is designed so that it at least partiallyabsorbs power reflected from the plasma process at the basic frequency.5. The plasma supply device of claim 1, wherein the at least one outputnetwork includes at least one inductance that has a planar technology.6. The plasma supply device of claim 1, wherein the printed circuitboard is produced from glass fiber reinforced epoxy resin.
 7. The plasmasupply device of claim 1, wherein the at least one output networkincludes at least one output transformer having a primary-side windingand a secondary-side winding.
 8. The plasma supply device of claim 7,wherein the at least one output transformer is planar.
 9. The plasmasupply device of claim 7, wherein the printed circuit board is ofmulti-layer design.
 10. The plasma supply device of claim 9, wherein theprinted circuit board has four layers, and a turn of the at least oneoutput transformer is formed in each of the four layers of the printedcircuit board.
 11. The plasma supply device of claim 9, furthercomprising through contacts formed on the printed circuit board forconnecting conductor paths arranged in the layers.
 12. The plasma supplydevice of claim 7, wherein the primary-side winding and thesecondary-side winding of the at least one output transformer each havetwo turns.
 13. The plasma supply device of claim 7, wherein the at leastone output network includes at least one set of first inductancesarranged between the input connection and the primary-side winding. 14.The plasma supply device of claim 7, wherein the at least one outputnetwork includes at least one impedance adapter element between thesecondary-side winding and at least one output connection for theconnection of a load, wherein the at least one impedance adapter elementincludes one or more of a second inductance and a capacitor.
 15. Theplasma supply device of claim 7, further comprising at least onemagnetic field strengthening element assigned to one or more windings ofthe at least one output transformer.
 16. The plasma supply device ofclaim 1, wherein the at least one output network includes at least oneinductance, and the plasma supply device further comprises at least onemagnetic field strengthening element assigned to one or more of theinductances.
 17. The plasma supply device of claim 16, wherein the atleast one magnetic field strengthening element is a ferrite.
 18. Theplasma supply device of claim 16, wherein at least one recess is formedon the printed circuit board for receiving the at least one magneticfield strengthening element.
 19. The plasma supply device of claim 1,wherein the at least one output network includes at least one inductancehaving a value greater than 50 nH and a quality better than
 200. 20. Theplasma supply device of claim 1, further comprising a cooling plateconnected to the printed circuit board.
 21. The plasma supply device ofclaim 20, wherein the printed circuit board is separated from thecooling plate.
 22. The plasma supply device of claim 20, wherein theprinted circuit board is separated from the cooling plate by a distancethat is in relationship to the thickness of a magnetic fieldstrengthening element enclosing one or more of inductances and windingsof an output transformer.
 23. The plasma supply device of claim 20,further comprising one or more heat transmission elements between theprinted circuit board and the cooling plate.
 24. The plasma supplydevice of claim 23, wherein the heat transmission elements are in thevicinity of the at least one output transformer, and conductor paths ofthe printed circuit board are guided through the magnetic fieldstrengthening element assigned to the at least one output transformer tothe heat transmission elements.
 25. The plasma supply device of claim 1,further comprising an earth connection on the printed circuit board. 26.The plasma supply device of claim 25, wherein the earth connection is abore through the printed circuit board having an electrical contact. 27.The plasma supply device of claim 1, further comprising two outputnetworks, each output network including at least a set of firstinductances, an output transformer, and an impedance adapter element,wherein the output powers of the two output networks are combined to onetotal power with a coupler.
 28. The plasma supply device of claim 1,wherein at least two output networks are present whose output powers arecombined to one total power.
 29. The plasma supply device of claim 28,wherein the output networks are connected to separate inverters.
 30. Theplasma supply device of claim 28, wherein the combination of the outputpowers is achieved by means of at least one coupler.
 31. The plasmasupply device of claim 30, wherein the at least one coupler is on theprinted circuit board and is designed at least partially in a planargeometry.
 32. A plasma supply system that generates an output powergreater than 500 W at an essentially constant basic frequency of greaterthan 3 MHZ for powering a plasma process, the plasma supply systemcomprising: at least two plasma supply devices, wherein each plasmasupply device includes at least one inverter connected to a DC powersupply, wherein the at least one inverter has at least one switchingelement, and at least one output network electrically coupled to the atleast one inverter, wherein the at least one output network is arrangedon a printed circuit board; and at least one coupler that combinesoutput powers of the at least two plasma supply devices.